The present invention relates to a method and an apparatus for generating a driving status signal in a motor vehicle.
Data that represent the acceleration of the vehicle relative to the road surface, i.e. the ground acceleration, are required, for example, in a spacing and speed control system in lines of vehicles. In such a system, the deceleration with which the vehicle must be braked in order to keep the spacing constant is calculated as a function of the vehicle speed and its spacing from the vehicle in front.
The ground acceleration, as well as the forces caused by a road surface inclined in the longitudinal direction, are also used in the braking control system, for example in electric-motor brakes or electrohydraulic brakes.
In present-day vehicles, in particular those with antilock braking, drive slip, and/or vehicle dynamics control systems, it is known to sense the rotational speed of the wheels, i.e. the wheel rotation speeds, using sensors. By differentiating over time, it is in principle possible to determine the acceleration of the vehicle relative to the road surface, i.e. the ground acceleration. Problems occur in this context, however, if the wheels exhibit a certain slip (drive slip or braking slip). In addition. determining the ground acceleration solely from the wheel rotation speeds is not fast enough.
If a longitudinal acceleration sensor is present on or in the vehicle, it is fast in terms of sensing the vehicle acceleration, and substantially linear with respect to the instantaneously acting braking force. The longitudinal acceleration sensor has the disadvantage, however, that it associates the ground acceleration additionally with the slope drag. The sensor thus measures not only the desired ground acceleration a_xc3xcGr but also acceleration components g*sin xcex1 that are caused by a road surface inclined in the longitudinal direction (with slope xcex1):
a_Sen=a_xc3xcGr+g*sin xcex1
The object of the present invention is to make possible, in simple fashion, the ground acceleration.
As already mentioned, the present invention is based on a method and an apparatus for generating a driving status signal that represents the driving status of a motor vehicle. According to the present invention, a wheel acceleration variable representing the acceleration of the vehicle wheels is formed. In addition, an acceleration variable representing the longitudinal acceleration of the vehicle is sensed by way of sensors. A feature of the present invention is that the wheel acceleration variable that is formed is low-pass filtered, and the acceleration variable that is sensed is high-pass filtered; and
the driving status signal is generated as a function of an association between the low-pass-filtered wheel acceleration variable and the high-pass-filtered acceleration variable.
The present invention makes it possible to determine the vehicle""s ground acceleration from a combination of the signals of an acceleration sensor and the wheel rotation speed signals. The combination according to the present invention of the two signals is necessary in order to compensate for the disadvantages, mentioned above, of the individual sensors.
In particular, provision is made for the driving status signal to be generated as a function of an additive association of the low-pass-filtered wheel acceleration variable and the high-pass-filtered acceleration variable. Filtration followed by addition of the two filtered signals, according to the present invention, makes it possible to generate a signal that correctly indicates the ground acceleration.
In a particularly preferred embodiment of the present invention, provision is made for the low-pass filtration and high-pass filtration to be accomplished with the same time constants.
As already mentioned above, it is particularly advantageous to utilize the driving status signal, once generated, to regulate and/or control the vehicle""s brakes and/or for spacing control and/or speed control purposes.
In particular, the driving status signal that is generated represents the acceleration of the vehicle relative to the road surface on which the vehicle is moving.